Daily Image

09-04-2010
PreviousNext
Click here or on the picture for a full size image.

How much gas do you need to make a radio galaxy?

Submitter: Raffaella Morganti
Description: Already since a few years, we have used quite a lot of WSRT time to study the presence of gas in galaxies that are strong radio continuum emitters (radio galaxies). We want to investigate whether the gas is the fuel that makes these galaxies more "active". The gas (neutral hydrogen) can also be used to trace the formation history of the galaxy. In particular, we wanted to see whether they are more likely the result of mergers of large galaxies rich in gas. It is commonly believed that the instabilities produced during such mergers brings the gas down to the central regions to fuel the central black hole active.

Our study finds that only a small fraction of radio galaxies can be actually associated to gas-rich merger events. The only possible candidates (out of a sample of 22 objects) are those shown in the figure above, where orange represents the distribution of the HI gas, white the optical galaxy. The conclusion is that large amounts of gas are not a necessary condition to fuel and to maintain a radio source active.

To first order, the overall HI properties of radio galaxies appear similar to those of radio-quiet early-type galaxies. If confirmed by deeper observations, this would imply that the presence of radio emission may just be a short phase that occurs at some point during the lifetime of many early-type galaxies. Mergers/interactions with small, instead of big, galaxies (or other processes like accretion of hot gas) could be a more common way to fuel the nucleus.

The analysis of these HI data is part of two PhD theses (Bjorn Emonts and Christian Struve) and the results have been presented in a number of papers.
The latest, by Emonts B., Morganti R., Struve C., Oosterloo T. et al., is now in press in the Montly Notice of the Royal Astronomical Society (see also http://arxiv.org/abs/1003.2835 ).
Copyright: Astron
 
  Follow us on Twitter
Please feel free to submit an image using the Submit page.